NAIROBI, Kenya – NATO’s anti-piracy force has found no crew members or pirates onboard a Danish cargo ship that Somali pirates hijacked and then abandoned, officials said Friday.

The MV Leopard was attacked on Wednesday by pirates in two skiffs but since then the ship’s owner, Shipcraft shipping company, has lost contact with its crew of six, said the company’s managing director, Claus Bech, in a statement Friday.

Turkish warship TCG Gaziantep, the vessel nearest where the attack took place in the Arabian Sea, went to investigate Thursday, said Jacqui Sherriff, spokesman for NATO’s anti-piracy force.

The Turkish warship sent a helicopter which overflew the ship, “and after some time it became apparent they couldn’t see anyone onboard,” Sherriff told The Associated Press on Friday. Sailors from the Gaziantep then boarded the MV Leopard and thoroughly searched the cargo ship but did not find any pirates or crew, she said.

The Gaziantep is currently watching the MV Leopard, which is about 500 miles from Oman’s port of Salalah, Sherriff said.

Bech said Shipcraft is in touch with “relevant authorities” to ensure the safe return of the crew – four Filipinos and two Danes. He said there’s no “reliable information” about their whereabouts.

With the attack on the MV Leopard and the hijacking of its crew, Somali pirates currently hold 28 vessels and about 660 sailors and other crew hostage.

Somali pirates attack vessels because of the multimillion dollar ransoms they are able to get. Piracy thrives because of Somalia’s lawlessness and its coastline runs along some of the world’s key waterways such as the Gulf of Aden through which an estimated 20,000 ships pass. Many of these also pass through the Arabian Sea.

Somalia has not had an effective central government for 20 years nor does it have a naval force that can tackle piracy off its coast. The ransoms the pirates get are among the few regular sources of income for small businesses that supply the pirates food and other goods.